The invention relates to a process for piecing-up a wrapped yarn which is produced by means of a hollow spindle from a spinning fiber bundle and a binding thread. A pair of delivery rolls of a drafting device feeds the spinning fiber bundle to the hollow spindle where the binding thread supplied from a binding thread bobbin is wrapped therearound. The wrapped yarn is drawn out of the hollow spindle and wound on a yarn bobbin.
It has previously been proposed for piecing-up during the production of wrap yarn to suck the untwisted spinning fiber bundle emerging from a pair of delivery rolls of a drafting apparatus into a hollow spindle by means of a compressed air gun, the binding thread being wound around and reinforcing the spinning fiber bundle (DE-OS No. 2,482,483). According to a further prior art proposal, the spinning fiber bundle is to be introduced from the pair of delivery rolls into the inlet opening of the hollow spindle with the aid of a feed tube supplied with compressed air (DE-OS No. 1,685,881).
Common to both proposals is the disadvantage that the piecing up of the spinning fiber bundle, which is liable to break as it is drawn along, is not guaranteed. Thus, in the first-mentioned process, it can occur that the speed of the compressed air in the gun is so high that the spinning fiber bundle is not bound in by the binding thread, or that, on the other hand, the reduced pressure produced in the hollow spindle is too small so that the binding thread is not drawn off from its bobbin. Difficulties arise with the reinforcement of the spinning fiber bundle and the introduction into the hollow spindle, jeopardizing the success of the piecing even when a feed tube supplied with compressed air is used.